In recent years, HSUPA (High Speed Uplink Packet Access) has been studied as a transmission standard for enhancing the uplink packet communication speed on W-CDMA (Wideband-Code Division Multiple Access). In HSUPA, E-DCH (Enhanced-Dedicated CHannel) is provided as a dedicated channel for the transmission of uplink packets.
Although a mobile station apparatus sends packets to a base station apparatus using E-DCH, since the appropriate transmission power for mobile station apparatus packet transmission differs according to the distance between the mobile station apparatus and base station apparatus, typically E-DCH transmission power control (TPC) is performed in the same manner as conventional uplink transmission power control. One example of a transmission power control method is the closed-loop transmission power control. With closed-loop transmission power control of an uplink, the base station apparatus measures the link quality using a signal received from the mobile station apparatus, compares the measured link quality with the target link quality, and transmits to the mobile station apparatus a TPC command that instructs an increase or decrease in the transmission power so as to bring the measured link quality closer to the target link quality. The mobile station apparatus then increases or decreases the transmission power in accordance with the TPC command transmitted from the base station apparatus.
However, during movement between cells covered by the base station apparatus, the mobile station apparatus sometimes performs a soft handover to communicate with a plurality of base station apparatuses. That is, for example, as shown in FIG. 14, when mobile station apparatus M is positioned near the border of cell C1 and cell C2, mobile station apparatus M communicates with both base station apparatus B1 which covers cell C1 and base station apparatus B2 which covers cell C2. At this time, when the above-mentioned closed-loop transmission power control is performed, mobile station apparatus M receives a TPC command from both base station apparatus B1 and base station apparatus B2. In such a case, the contents of the respective TPC commands transmitted from base station apparatus B1 and base station apparatus B2 may conflict due to the difference in the propagation environment of the receptive cells.
Here, with the technology, for example, disclosed in Patent Document 1, when TPC commands are transmitted from a plurality of base station apparatuses during a soft handover and at least one of the base station apparatuses instructs the mobile station apparatus to decrease the transmission power, the mobile station apparatus selects the TPC command of that base station apparatus to decrease the transmission power. That is, in the above-mentioned example, as shown in FIG. 15, when at least base station apparatus B1 or base station apparatus B2 transmits the TPC command “Down,” which instructs decrease in transmission power, the transmission power of mobile station apparatus M is decreased. Only when both base station apparatus B1 and base station apparatus B2 transmit the TPC command “Up”, which instructs an increase in transmission power, the transmission power of mobile station apparatus M is increased.
The method is referred to as the “or of down” method where a mobile station apparatus, upon receiving TPC commands from a plurality of base station apparatuses, selects the TPC command of the base station apparatus to decrease the transmission power if “Down” is transmitted from at least one such base station apparatus as described above. According to the “or of down” method, even though the mobile station apparatus has excessive transmission power for only one of the base station apparatuses (i.e., the base station apparatus that transmits the “Down” command) of a communication party, the mobile station apparatus will not further increase the transmission power, thereby preventing a great increase in interference in the overall system and increasing subscriber capacity.
In addition, in Patent Document 2, a method is disclosed where the mobile station apparatus measures the link quality of the downlink and then applies the “or of down” method while ignoring the TPC commands transmitted on downlinks of inferior link quality.    Patent Document 1: Japanese Patent Application Laid-Open No. HEI8-18503    Patent Document 2: Japanese Patent Application Laid-Open No. HEI9-312609